Nice work! I appreciate the time you put into describing your workflow.

So you have 4 other voices to repair and calibrate? And they need a 2nd motherboard to drive them?

I can totally relate after just having finished restoring a Prophet 600 whose midi wasn't working - at one point I even killed the whole thing when I blew a CMOS chip that prevented the MUX from cycling through the analog inputs Then I also blew another CMOS that buffered 2 of the bits 16 bits going to the DAC... I noticed something was amiss when the keyboard couldn't scale properly and used a logic probe to check which of the 16 DAC inputs weren't pulsing.

After being totally frustrated, I sat down and calmly decided it would be a learning experience and everything proceeded well after that point.

I think the key to working on this vintage of synth is a lot of patience and tracing out the logic workflow carefully to try to understand exactly what is happening.

Good luck with the rest of this restoration! So nice to see one of these old classic beasts resurrected._________________Sneak-Thief - raw electrofunk

After being totally frustrated, I sat down and calmly decided it would be a learning experience and everything proceeded well after that point.

That may be the single best piece of advice for troubleshooting synths I've seen

I know that method tends to work for me, though often it also takes a couple days of doing something unrelated to forget the detail of the frustration, otherwise I tend to get hung right back up in it again.

thanks for the information!
I did the same kind of work one mine ( a four voices upgraded to six voices) last year and I still have some problems here and there.

I have two issues I can't solve:
> voice boards pitches are shifted randomly when cross modulation is activated, so if the same note is repeated several times it plays an arpeggio
> SH LFO amplitude is too weak, and I can't see what IC does the job.

Could it be related to the 4051 you're pointing in your description?
I don't see what 4051 it is exactly, the SH part of the shematic is really not clear to me.

Thanks in advance for your help. And sorry for asking: information on this synth is too rare to miss a chance to learn more.

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